1. Technical Field
The present invention relates to methods and apparatus for welding metal sheets in general, and to methods and apparatus for controlling the gap between the metal sheets being welded in particular.
2. Background Information
Laser welding is now in widespread use as a process for joining metal sheets together. In this process the sheets are preferably butt jointed, with their edges positioned so that there is only a narrow gap between the sheets. To obtain a weld seam of high quality, the gap between the sheets to be joined should not be wider than 0.05 or 0.08 mm, and the deviations of each individual sheet should not exceed one half of these maximum permissible widths of gap. It is obvious that in order to observe such tolerances, correspondingly expensive tools, or complicated machining methods, are necessary.
It is known from European Patent Application No. EP 0565846 when welding straight seams to plastically deform at least one of the metal sheets with a squeeze roller before or in the welding zone so that the maximum permissible width of gap between the sheets to be joined is not exceeded. In connection with this known teaching, a series of embodiments are described which relate in particular to the varied configuration of the squeeze rollers.
The known teaching is only suitable for straight weld seams. In particular it is unsuitable if there is a requirement to guide the weld seams along a given line, as in such cases the squeeze rollers proposed in the known teaching generate lateral forces which can lead to undesired distortions of the metal sheets.